Arkansas tried that in response to the federal courts' desegregation rulings in the 1950s, and President Eisenhower federalized the Arkansas National Guard to enforce the federal courts' orders.
Before anyone flames me, I am not comparing same-sex marriage to desegregation; I am just pointing out that a state can't decide on its own to nullify a federal court order, if the President is willing to enforce that court order.
You mean a state can't successfully nullify a federal court order because it doesn't have the firepower. A state certainly has the right to refuse a clearly unconstitutional federal law or order. Well, I say let the fight begin. It's time to start drawing lines and saying enough already to the on-going coup of our constitutional republic. I'd rather lose the fight for freedom than to stand meekly by while the descendants of King George create a tyranny.